Howdy! I'll start by giving you a brief primer on chocolate malt. Chocolate malt is not actually chocolate in flavor. It is regular old malted barley that is roasted until it produces a nice dark chocolate color and sometimes aroma. You're mostly going to get a lightly roasty and nutty flavor from it. That being said, if this is your first attempt with it, I wouldn't do any more than a half pound as when a beer gets too roasty it tends to get more bitter. A half pound will allow that roasty toastiness to be present but likely not overpowering.
So if you do want a chocolate flavor to the beer I'd stick with the coco powder. Not that chocolate malt would be bad in this beer, I think it goes well with coffee flavors, but it may not be what you're looking for.
Check out this guide below, this details the different malts and what they're good for.